Telephone system



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1m? LanBEIFI'MEFHE Elf UPSET! 0 O Fr o o a 8n o 1 5m Om TELEPHONE SYSTEM Filed April 25, 1928 10 Sheets-Sheet 10 n N g N Ifir-EFIFF L annlfil' NEH 1 Sign sun Patented Mar. 10, 1931 entree stars-s Parser @FFECE LANCELO'I." MARTIN SIMPSON, OF LEEDS, ENGLAND, ASSIGNQR '10 AsSOG IATED TELE- PHONE AND TELEGRAPH COMPANY, OF KANSAS CITY, MISSOURI, A. CORPORATION OF DELAWARE TELEPHONE SYSTEM Application filed April 25, isea'ser a No. 272,609, and in Great Britain May 11,1927.

The present invention relates to telephone systems and is more particularly concerned with apparatus for performing sorcalled routine tests. It is generally realized that with complicated apparatus of the type used in automatic telephony it is desirable that each piece of apparatus should be tested periodically to make sure that it is fulfilling all its functions, since by this means faults may be brought to light and corrected be fore they occur in the actual setting up of connections by subscribers. The present invention is particularly applicable to the testing of register senders" of the kind adapted to respond to impulses of one type sent in and thereafter to transmit impulses of another type, but certain of its features are capable of more general application.

In order that the routining shall be properly effective it is important to make sure that each piece of apparatus shall be tested, and since in the general way the apparatus will be available for use by subscribers'at the time the routine test-is made it may be necessary for the routiner to wait in association with a particular piece of apparatus until it becomes free. According to one feature of the present invention, if a piece of apparatus is found busy when it is seized by the row tiner, this waits for a definite time interval and if the apparatus has not been-returned to common use at the end of this period, an alarm is given and the particular apparatus indicated, and at the same time the routiner seizes the next piece of apparatus so that the test can continue without wasting an undue amount of time in case the attendant is not able to look into the fault immediately;

7 It is also very usual in routining apparatus of the kind considered to make special arrangements for routining a particular piece of apparatus a number of times as might be desirable for instance in case it had originally developed a fault which had subsequently been rectified by the attendant;

In previous arrangements of this type after the operation of the special key for effecting continuous routining, it has been usual for the attendant to operate special stepping keys to step the distributing switches .into

engagement with the particular piece of apparatus under conslderation. According to another feature of the lnvention, however,

the necessity for this operation is obviated in that'a special jack field is provided and when the attendant wishes to perform a continuous routine of any piece of apparatus he inserts a plug in the jack associated there with and then operates the continuous routine key whereupon the distributing switches hunt automatically to find the piece of apparatus in question. 1

The invention will. be better understood from the following description of one method of carrying it into effect which is given by way of exan'iple. This arrangement is intended to test the so-called coders used in the call indicator arrangement described in the patent of W. O. Passmore, No. 1,716,563 issued June 11, 1929. Reference to this specification will show that a coder is associated with the outgoing end of a junction extending to a manual exchange when the associated repeater is taken into use and that the digits subsequently dialled by a subscriber are reg istered in turn in the coder. When the operator at the manual exchange is ready to receive the call, a certain switching operation is performed at the incoming end of the junction and thereupon the coder commences to send code impulses corresponding to the digits received. A routiner for testing such coders must therefore incorporate an arrangement in which impulses are sent to the coder and the special code impulses sent out therefrom are received on appropriate storage relay groups. r r

Referring now to the accompanying drawings comprising Figs. 1 to 10 inclusive, Figs. 1 to 6 and Fig. 8 show various relays controlling the operation of the routining equipment; Fig. 7 shows the countingswitch CGS and also the control switch CS which determines the digits which are impulsed into the coder; Fig. 9 shows the primary distributor PD to the banks of which a. suitable number of secondary distributors SD are connected,

and also shows the busy marking switch BS time; while Fig. 10 shows the sending switch SES, the test switch TES, and the pause timing switch PTS which ensures the correct pause between the sending of digits.

Access to the various coders from the routining equipment is obtained by means of the primary and secondary distributors, the secondary distributors being advanced one step when coder has been completely tested so as to connect up the next coder, and the primary distributor being also advanced one step when all the coders accessible from one secondary distributor have been dealt with.

hen it is desired to carry out a test the attendant will operate the start key 10, Fig. 6, thereby energizing slow-to-pull-up relay ST and also closing a circuit over the back contact 11 of relay ST, springs of continuous routine key 12, conductor 13, driving magnet DMl of the primary distributor PD to battery. When relay ST is fully operated, this circuit is opened and the magnet de-energizes moving the wipers of the primary distributor PD into contact with the first secondary distributor SD. At armature 14 relay ST closes a circuit from earth on resting contact of armature 15, conductor 16, working contact of armature 14, slow-to-pull-up relay ORR to battery, and also over the resting contact of armature 17, conductor 18, wiper 19 and first bank contact of the primary distributor PD, driving magnet DM2 of the secondary distributor SD to battery. This circuit is maintained during the slow operating time of relay CRR and when relay GER is fully operated is broken so that the driving magnet DM2 releases and moves the wipers of the secondary distributor forward one step so that they are now in engagement with the first coder.

It will be understood that conductors from the coders are connected to the banks of the secondary distributors and it will be assumed that the release trunk conductor is wired to bank 32, the pulse conductor to bank 105 and the negative and positive lines to banks 131 and. 144 respectively. At armature 2O relay ST operates relay STR; at armature 21 prepares the operating circuit for relay A when the first coder is available for testing; and at armatures 22, 23 and 31 opens the homing circuits of the test switch, the pri mary distributor and the sending switch respectively.

Relay STR upon operating at armature 25 earths the motor start conductor 26, While at armature 27 a point in the homing circuit of the secondary distributor SD is opened. It should be understood that there will be sufiicient contacts such as 27 and 28, 29 and 30 on relays STR and CR to provide homing circuits for all the secondary distributors which may be equipped.

As the coders will be available for common use during the time that routining operations are carried out, it will be appreciated that the particular coder on which the secondary distributor wipers are now standing may be in use on a regular call. The routining equipment will therefore wait for a time interval and commence its testing as soon as the coder again becomes free. As the holding time of a coder in the setting up of a regular call is comparatively short, the testing will be commenced after only a brief wait, but if the holding time becomes excessive, as for instance, if the coder has been artificially busied, the routiner will step to the next coder and commence testing thereon. The busy marking switch BS will then rotate to contacts associated with the coder found busy and cause the associated lamp to flash and an alarm to be brought into action thereby calling the attention of the attendant. In the meantime, testing will proceed on the other coders, but if a second busy coder is encountered the testing will be stopped and an urgent alarm signal operated.

Assuming first that the first coder is busy, the: guarding earth from the release trunk conductor of the coder will be extended over bank contact and wiper 32 of the secondary distributor, bank contact and wiper 33 of the primary distributor, conductor 34, springs of key 35, conductor 36, working contact of armature 21, conductor 37, resting contact of armature 56, winding of relay A to battery. Relay A operates and at armature 39 opens a point in the energizing circuit of relay B, while at armatures 40 and 41 circuits are. prepared for relay TP by means of which the alarm will be brought into operation after a time interval. The action of the busy marking switch to indicate this coder it it is held busy for more than a predetermined time will be described later, as also will the operation of the alarm circuits, and it will now be assumed that the coder is returned to common use almost immediately. Relay A will thereupon release as the guarding earth is removed and relay B will operate over a circuit which may be traced from earth, working contact of armature 4.10 of relay ST, conductor 42, wiper 43 and first bank contact of the test switch TES, conductor 44, resting contacts of armatures 39 and 4-5, winding of relay B to battery. Relay B operates, thereupon at armature 46 closing a locking circuit tor itself over resting contact of armature 47, conductor 48, working contact of armature 20 to earth, and at armature 49 completing a circuit to operate relay SDD, "from the earth on wiper 50 of the test switch TES and its first bank contact, normal contacts of cancel test No. 1, key 51, conductor 52, working contact of armature 49, conductor 53, winding of relay SDD tobattery. The operation of relay l3 also extends earth by Way of both windings of relay PS, Fig. 3, in series, resting contact of armature 54, conductor 55, working contact of armature 56 of relay B, conductor 37, working contact or" armature 21, conductor 36, key 35,'conductor 34, Wiper and bank contact of the primary distributor, wiper 32 and bank contact of the secondary distributor to the release trunk conductor of the coder, and thence to battery through a relay in the coder circuit. Relay PS now operates, thus short-circuiting its upper high resistance winding .at armature 57 and there by maintaining a low resistance earth on the guarding conductor of the coder to mark it busy, and the relay connected to the release trunk in the coder operates and prepares various holding and operating circuits for the coder storing, switching and controlling relays. Relay B also causes the operationot relay SS at armature 58 from earth, wiper 59 and bank contact of the control switch CS, Fig. 7, conductor 60, working contact of armature 58, resting contact of armature 61, winding of relay SS to battery, and also at armatures 62, 63 and 64 extends various test ing leads to the-wipers of the primary distributor. At armature 65 earth is extended from resting contact of armature 66 over conductor 67 to wiper 68 of the test switch and thence to an indicating lamp to indicate which test is in progress, so that as the test switch advances'to initiate the different tests the corresponding lamps will be lit from successive bank contacts. It will also be noticed that earth is extended from resting contact of armature 69 of'relay CR, Fig. 6, conductor 70, wiper 71 and bank contact of the primary distributor PD, wiper 72 and bank contact of the secondary distributor SD to an indicating lamp, so that a visual indication is afforded of the particular coder under test. r

The operation of relays SS'and SDD prepares a circuit extending from earth, work ing contact of armature 73, conductor 74, working contact of armature 75, conductor 76, resting contacts of a-rmatures 77 and 7 8,;

lamp 405, upper low resistance winding of relay PSS to battery. It will be remembered, however, that relay PS has just operated from the release trunk of the coder, thereby opening a point in the above circuit at armae ture 77 so that relay PSS will not operate. Assuming, however, that due to some fault in the release trunk circuit of the coder, relay PS does not operate, the circuit for relay PSS will be complete and the operation of relay PSS will energize relay FA atarmature 80, and the latter relay will then bring in an alarm as will be described later.

The operation of relay SS also extends earth from the working contact of armature 130, conductor 131, first bank contact and wiper 132 of the control switch CS, interrupter springs, driving magnet DM4 to battery, thus causing the control switch to step to its second contacts. This earth from armature 130 is also extended over conductor 133, resting contact of armature 91, conductor 92, to relay RA which therefore operates. Further, earth impulses from the impulse springs 81, which are conveniently operated 10 times per second, are connected over resting contact of armature 82, working contact of armature 83, conductor 84, resting contact of armature 85, lower winding of two-step relay PA to battery. Relay PA initially operates partially in the well-known manner and operates fully when the impulse springs open, thereupon at armature 85 switching the earth impulses to the driving magnet DM3 of the sending switch SES, Fig. 10, over conductor 86, resting contact of armature 87 and conductor 88. The locking circuit for relay PA is from earth, resting contact of armature 117,working contact of armature 118, conductor 119, resting contact of armature 116, conductor 134, workingcontact of armature 135, both windings of relay PA in series'to battery. The wipers of the sending switch will therefore be stepped round thebank, and as they step to the second set of contacts, earth extended from second bank contact and wiper 89 over conductor 90 operates relay SA. At armature 93 relay SA lights the lamp 128 to indicate thatthe routining equipment is in the process of sending a number into the coder at armature 91 opens the initial operating circuit of relay RA and at the working contact of the same armature connects earth pulses also atv the rate of 10 'from' earth, working contact of armature 93, conductor 94, resting contact of armature 95 during those periods that relay RA is normal, conductor 96, resting contact of armature 97, conductor 98, working contact of armature 99, con'ductor 100, resting contactof armature 101, conductor 102, working contact of armature 63, conductor 103, wiper 104 and bank contact of the primary distributor, wiper 105 and bank contact of the secondary distributor to the pulse lead to the coder under test. As relay RA impulses therefore, earth will be connected anumber of times to the pulse conductor of the coder. The sending switch is stepping round its bank during this time and as it reaches its sixth contact earth is extended from wiper 106 of the control switch, first bank contact, conductor 107, resting contact of armature 108, conductor 109, sixth bank contact and wiper 110 of the sender switch SES, conductor 111, winding of relay SZ to battery. Since springs 81 and 413 open and close in synchronisni it will be seen that by the operation of relay RA tour impulses have been transmitted to the coder and now the operation of relay SZ opens the circuit to the pulse conductor at armature 97. At armature 112 earth is extended to maintain relay RA in the operated position to prevent an additional impulse being sent; at armature 113 a locking circuit is closed for relay SZ over conductor 114, contacts of the pause timing switch bank and wiper 130 to earth over conductor 42 and armature 410 of relay ST; at armature 87 the stepping pulses are disconnected from the magnet DM3 of the sender switch; at armature 115 the circuit to return the sender switch to its home position is closed from earth, wiper 89 and bank contacts, conductor 90, working contact of armature 115, conductor 414, interrupter springs, magnet DM3 to battery, at armature 116 a point in the locking circuit of relay PA is opened and relay PA releases; at armature 120 earth is extended over conductor 121 to the magnet DM4 of the control switch, so that the magnet is held energized, and at armature 122 earth pulses, at con- Veniently the rate of 20 per second, are ex tended from conductor 123 to two-step relay QX which operates in known manner, locking itself at armature 124 to earth at armature 112 and extending the earth pulses at the working contact of armature 125 to conductor 126 and thence to the driving magnet DMS of the pause timing switch.

In consequence of the completion of the circuit traced above, the sender switch is returned to its normal position and thereupon relay SA releases as its circuit is opened. Relay RA, however, remains energized over the back contact of armature 91 to earth at the front contact of armature 130 over lead 133, but relay RB releases as its circuit is opened when SA restores. The pause timing switch magnet will now step the wipers round the bank, under the influence of the earth impulses at 20 per second, and when it has made a predetermined number of steps, in the case of the connections shown in the drawing six steps, the holding circuit of relay SZ is opened anu relay SZ releases, disconnecting the stepping pulses from the driving magnet DM8 and allowing relay QX to release. Moreover the control switch magnet DEM will now de-energize and advance the wipers to the taird set of contacts and, further, at the back contact of armature 87 the locking circuit of two-step relay PA will be closed so that relay PA will lock up and again connect impulse springs 81 to the magnet of the sender switch. The wipers of the sender switch will accordingly be stepped round the bank again and relays SA, RA and RB will operate as before so that impulses will be sent to the coder over the pulse conductor. When four such pulses have been sent, the wipers of the sender switch will encounter earth from the control switch wiper 106, third bank contact, conductor 125, resting contact of armature 126, conductor 109, and thence as previously traced, causing the operation of relay SZ and'consequently causing the homing of the sending switch, operation of the pause timing switch, and stepping of the control switch as has just been described. These operations will be repeated in all live times, the connections on the control switch bank permitting the same number of impulses to be sent each time till the stepping of the control switch after the release of relay SZ following the fifth train of impulses extends earth from wiper 106, seventh bank contact, conductor 12?, winding of relay SC to battery, and the operation of relay SC at armature 82 disconnects earth impulses from the two-step relay 1 A and the sending switch magnet. The number which has thus been impulsed to the coder is 44444, of which the first digit serves to effect the selection and connecting up of compensating resistances in the coder so that the retransmitted coded pulses may always be effective over substantially the same junction resistance, while the remaining four digits represent a wanted subscriber-s number. The operation of the pause timing switch in the manner described ensures a definite pause between each train of impulses, thereby ensuring that the necessary switching operations take place in the coder before the next train of impulses is transmitted. The length of this pause may be altered it so desired by altering the connec tions on the banks of the pause timing switch.

The number that has ust been transmitted is stored in the coder and prepares circuits therein so that the number may be trans mitted in the form of directional current impulses conveniently known as light negative, positive and heavy negative, as is fully described in the Passmore patent previously referred to. As soon as the coder is seized, battery and earth are connected to the line leads from the coder. These battery and earth connections are through the windings of retard TR and may be traced from the positive line from the coder, bank contact and wiper 131 of the secondary distributor SD, bank contact and wiper 132 of the primary distributor PD, conductor 133, working contact of armature 64, conductor 134, resting contacts of armatures 135 and 136, conductor 137, resting contact oi? armature 138, conductor 139, lower winding of retard TR to battery, and earth through the upper winding of retard TR, conductor 140, resting contact ott' armature 141, conductor 415, working contact of armature 62, conductor 142, wiper 143 and bank contact 01' the primary distributor PD, wiper 144 and bank contact of the secondary distributor SD, to the other line to the coder.

Under the conditions of a normal call the coder will not send while there is battery and earth on the lines and waits for the removal of these connections by a switching operation at the distant end of the junction indicating that the equipment is prepared for the reception of coded pulses. In order to check that the coder does not send prematurely the routining equipment is arranged so that a delay takes place before permitting the coder to send. It will be remembered that relay SDD operated as soon as relay B operated, and now earth over wiper 106 and seventh bank contact of the control switch CS, conductor 127 and working contact of armature 145 operates relay SDR. Relay SDR upon operating extends earth pulses at conveniently the rate of one pulse every four seconds from conductor 146 over working contact of armature 147, conductor 148, resting contact ofarmature 149, upper winding of two-step relay DLP to battery. Relay DLP closes its light armature 150 thereby preparing-a locking circuit for itself which will become effective at the conclusion of the pulse. When this occurs relay DLP operates fully and is maintained from earth, working contact of armature 152, conductor 151, working contact of armature 150, both windings in series to battery. An indicating lamp circuit is also closed from earth at armature 153, conductor 154, resting contact of armature 155, lamp to battery, to indicate the state of the test. The next earth impulse received will operate relay DL over the working contact of armature 149, and resting contacts controlled by armature 156. Relay DL upon operating closes a locking circuit for itself at armature 156 to conductor 127 and earth at the control switch wiper 106; at armature 155 opens the indicating lamp circuit; at armature 157 prepares the circuit for the relays LN, LP and HN and at armatures 138 and 141 disconnects the line leads from the coder from battery and earth through retard TR and transfers them to the relays LN, LP and HN. This removal of current from the lines allows the coder to start transmitting the number in the form of coded pulses, which will be received and re corded by the routining equipment. It will be noticed that a time interval takes place before retard TR is disconnected and the coder is permitted to send, and this delay serves to check that the coder does not send prematurely. As soon as the coder commences to send it connects a guarding earth to the release trunk conductor, and if sending shouldtake place prematurely this earth will shunt relay PS which will then release, completing a circuit from earth, working contact of armature 73 of relay '88, Fig. 5, conductor 74, working contact of armature 75, conductor 76, resting contacts of armatures 77 and 78, lamp 405,

upper winding of relay PSS to battery. Relay PSS energizes, thereby closing a circuit for the lower winding of relay FA at armature 80 and a locking circuit for itself at armature 29. Relay FA brings in the alarm circuit, while the glowing of the lamp .405, which is maintained from the earth on the release key over conductor 1230 and armatures 229 and 80, in series with the upper low resistance winding of relav PSS, indicates the nature of the trouble- It will be seen, however, that as soon as relay DL operates to disconnect relay TR from the lines, a point is opened in the ener izing circuit of relay PSS at armature 7 8, so that when the coder functions correctly, that is waits till battery and earth are removed from the lines before sending, the release of relay PS when the release trunk is earthed by the coder at that stage is ineffective.

Assuming that the coder functions correctly, the coded pulses sent out will be received by relays LN, HN and LP, which are adapted to respond to currents in certain directions and of certain magnitudes only. Thus relay LN operates with a light negative pulse, and LP with a light positive pulse, that is, a pulse of similar strength but in the reverse direction, while a heavy negative pulse that is a pulse similar to a light negative pulse but of greater strength will operate both relays LN and HN. A light negative pulse, however, is not of sufiicient strength to operate relay HN which is marginally adjusted. The code corresponding to the digit 4 consists of a light negative pulse, a light positive pulse and a second light negative pulse, and this combination will be sent out four times to give the number 4444. The circuit of relays LN, LP and HN across the. leads from the coder may be traced from bank contact and wiper 1310f the secondary distributor SD, bank contact and wiper 132 of the primary distributor PD, conductor 133, working contact of armature 64, conductor 134, resting contacts of armatures 135 and 136, conductor 137, Working contact, of armature 138, conductor 160, winding of relay IO, resting contact of armature 161, conductor 162, working contact of armature 157, conductor 163, windings of relays LP, HN and LN in series, resting contact of armature 164, conductor 165, working contact of armature 141, conductor 415, working contact of armature 62, conductor 142, wiper 143 and bank contact of the primary distributor PD, wiper 144 and bank contact of the secondary distributor SD and thence to the coder. The first pulse received from the coder, which will be a light negative pulse, will operate relay LN thereby extending earth from working contact of armature 20 of relay ST, conductor 48, resting contact of armature 47, conductor 167, working contact of armature 168, conductor restores.

169, working contact of armature 170, conductor 171, resting contact of armature 172, upper winding of two-step relay Q11, resistance 175 to battery, and also to the winding of relay QS to battery by way of resting contact of armature 176. Relay (.ZS operates and prepares a locking circuit for relay QA which will become etlcctii'e when relay LN restores. As soon as relay LN restores, the earth on conductor 109 is extended over working contact 174, both windings of relay QA in series, resistance 175 to battery, causing relay QA to operate fully. Relay QS is maintained at this stage by this earth through tl e lower winding of relay QA, resting contact of armature 176, relay QS to battery. The next pulse received which is a light positive pulse, operates relay LP thus extending the previously traced earth on conductor 169 over working contact of armature 177, conductor 1'78, working contact of armature 179, conductor 180, resting contact of armature 181, upper winding of storing relay MY to battery. Relay MY operates and at armature 182 closes a locking circuit for itself to conductor 183 and the earth on conductor 109 as previously traced. The next pulse receiveda light negative-extends earth over armature 170, conductor 171, working contact of armature 172, upper winding 01' two-step relay Q2, resistance 19 1 to battery. Relay QZ closes its light armature 185 and as its lower winding then short-circuited it will remain in this condition till relay LN The earth that energized the upper winding of relay QZ is also extended to relay XM over conductor 186, resting contact of armature 187, winding of relay XM to battery, and relay XM closes contacts 188 to prepare an operating circuit for switching relay MS which, however, cannot yet operate due to the fact that it is short-circuited. lVhen relay LN restores after the pulse, the short-circuiting earth is removed and relay MS operates in series with relay Xld which also remains in the operated position, the holding circuit "for these relays being from the earth on conductor 183 as previously traced. The release of relay LN also allows relay 2.51 to operate completely and lock itself over both its windings in series, working contacts of armatures 185 and 17 1, conductor 169, to earth over the circuit already taced. The complete operation of relay QZ however opens the holding circuit of relay QS at armature 17 G and QS releases in turn thereby opening the holding circuit of relays QA and QZ at armature 174 so that these relays restore also. The three relays QS, Q11 and QZ are now normal and ready for further impulses. The operation of relay MS, Fig. 1, transfers the leads from the first group of storing relays MW, MX, MY and ME to the second group CV1, CK, CY and CZ at armatures 187, 189, 181 and 190, and the second digit to be received (which is alsoxl) will cause the operation 01 relays LN and LP, QS, QA and Q2 in exactly simila manner to that just described, though this time relay CY of the second storing group will be operated and relays X0 and US will be energized there after to eii ect the switching of the leads to the third group, which comprises relays D11 DX, DY and DZ and switching relays X1) and DS. The third and fourth di its will be received in similar manner causing the operation of storing relays DY and UY in the third and fourth storing groups res )ectivcly, the operation of relay BS switching the leads from the third to the fourth group, and relay US operating on the completion of the coded pulses, that is, after the reception of the last digit.

When relay DL operated, it extended earth pulses, conveniently every two seconds, from conductor 191, working contact of armature 192, conductor 198, resting contacts of armatures 19 1 and 195, lower winding 01? two-step relay Q to battery, and the first pulse received will cause relay Q to close its light armature 196. At the termination of the pulse, relay Q, will operate fully and will then be maintained from earth, working contact of armature 197, conductor 198, working contact of armature 196, upper winding of relay Q, resting contact of armature 195, lower winding to battery. As soon as relay US operates after the storing of the fourth di it, earth is extended from resting contact o't armature 208 of relay CD, Fig. 5, conductor 209, working contact of armature 210, conductor 211, winding of relay S to battery. Relay S operates and at armature 195 opens the circuit of relay Q allowing it to release, and at armature 246 extends the earth from armature 208, conductor 209 and conductor 200 to contacts of the storing relays and thence to indicating lamps. As the digit 4'.- was received by each group, and thus relays MY, CY, DY and UY respectively are operated, the earth on conductor 200 will be extended for instance in the third group, over resting contacts of armatures 201, 202 and 203, working contacts of armature 201, lamp 4, conductor 205, resting contact of armature 206, resistance 207 to battery, and also via similar circuits in the other groups to con-ductor 205 and battery. Therefore the number 4444 will be displayed on the panel situated adjacent to the routining equipment, thus providing a visual indication that the correct number has been received.

The operation of relay S also connects earth impulses from conductor 191, working contact of armature 212, conductors 213, resting contact of armature 416 to two-step relay TS which operates in the well-known manner locking to earth on working contact of armature 214; over conductor 215 and arma ture 216, and extends the next pulse to twostep relay TSR, which in turn extends the succeeding pulse to relay 'CD over resting contact of armature 217 and conductor 218. Relay CD operates in due course and locks itself at armature 219 to earth at armature 220 of slow relay SS; at armature 61 opens the circuit of relay SS, at armature 208 removes earth from relay S and the display lamps so that relay S restores and the lamps are extinguished; at armature 286 completes a holding circuit for relay ET, the function of which is described later; at armature 66 removes earth from the indicating lamp lighted over wiper 68 of the test switch, and at armature 221 extends earth over conductor 222 to energize the driving magnet DM5 of the test switch TS. When relay CD restores on the release of relay SS, the magnet DM5 will de-energize and move the wipers to the second set of contacts and now, therefore, the second test indicating lamp will be lit. The releasing of relay S allowed relays TS and TSR to restore and the circuits are now prepared for the commencement of the second test. Before the description of the next test is taken up it will be convenient to consider the results of incorrect sending by the coder. Several possibilities may arise, for example, no pulses at all may be received by the storing relays, due perhaps to premature sending as mentioned earlier, or a number may be partially set, or it may be sent incorrectly and a wrong display result.

To take the first case, if no pulses are received, none of the group switching relays MS, CS, DS or US will be operated and therefore relay S will not operate to open the circuit of two-step relay Q. Consequently, the next pulse received over conductor 191 will operate relay QR over the working con tact of armature 194 and resting contacts controlled by armature 244, and relay QR will lock itself at armature 244 to earth on key 231 over conductor 247. A circuit is now completed from earth, resting contact of armature 223 of relay NC, Fig. 8, conductor 224, working contact of armature 225, conductor 226, resting contact of armature 227, lamp 228, conductor 235 to battery through the low resistance upper winding of relay FA. Relay FA operates and at armature 229 locks itself over conductor 230, springs of key 231, resting contact of armature 233 to earth. At armature 234 an alarm lamp 332 is lit and an audible signal BL energized. The test cannot proceed any further and the signal will call the attention of the attendant, who must operate key 231 before relays QR and FA can be released. The glowing of the no pulses received lamp 228 indicates the nature of the trouble. It Will be appreciated that the period of the earth pulses on conductor 191 is such that ample time is allowed for the storing relays to be set up and relays US and S operated when, in the normal case,

the coded pulses are completely received before the next pulse occurs to operate relay QR, and as the operation of relay S releases two-step relay Q, there is thus no possibility of the alarm being falselygiven.

In the case Where'all of the pulses are not received, the switching relay MS of the first storing group will be operated, but the switching relayUS of the last storing group will still be normal. As before, therefore, relay Q, will remain operated and relay QR will be energized in due course and relay FA will now be energized in series with lamp 236 and the working contact of armature 227, conductor 226, working contact of armature 225, conductor 224, rest-ing contact of armature 223 to earth. Relay FA operates and locks itself to bring in the alarm as before, while the glowing of number partially received lamp 236 indicates the nature of the trouble. I 1 I In the case of the number being incorrectly transmitted and a wrong number resulting on the display lamps, it will be seen that the battery feed to all display lamps in each set except the fourth is at this stage from conductor 237 and the winding of relay WN. As lamps 8 are used for further tests at a later stage, their battery circuit it will be noted extends from relay WN over conductor 238, resting contact of armature 239, and conductor 240. If therefore any pulses are incorrectly transmitted, a circuit for a lamp other than 4 will be closed when relay S operates and consequently relay WN will be energized. Thereupon at armature 241 earth is extended fromresting contact of armature 250 by way of wrong number lamp 243 and conductor 418 to the low resistance upper winding of relay FA and relay FAenergizes to bring in the alarm circuit asbefore.

A further operating feature of the coder circuit that is checked at'this stage is the connecting of earth by the coder to the release trunk conductor as soon as it starts sending. This is to ensure that'if the calling subscriber clears down while the coder is sending the coder is guarded until the sending switch has completed its operation and returned to normal. The earth placed on the guarding conductor by the coder at this stage shunts down relay PS, as previously described, but the release of this relayis now without effect as the operating circuit for relay PSS is open at armature 78 of relay DL. It will be seen that as soon as the coder has sent the first digit and relay MS operates to switch the leads to the second storing group, a circuit is closed from earth, working contact of armature 275, resting contact of armature 276, conductor 277, winding of relay Z to battery. Relay Z operates and at armature 278 closes a looking circuit for itself over resting contact of armature 279, conductor 133 to earth at armature 130. At armature 280 relay Z prepares an alarm circuit, and at the working contact of armature 5% the release trunk conductor of the coder under test, which is connected to the bank of wiper 32 of the secondary distributor, is transferred to the lower winding of relay ET. If the release trunk is not earthed at this time relay ET will not operate and as soon as relay CS operates after the reception of the second digit earth is eX- tended from armature 281, conductor 282, resting contact of armature 283, lamp 2841, low resistance winding of relay FA to battery to brin in the alarm as usual, the lamp 284 indicating the nature of the fault. If, however, the release trunk is correctly guarded, relay ET will operate, locking itself on its second winding at armature 285 to earth on conductor 169 and opening a point in the alarm circuit at armature 283.

At the conclusion of sending the code, the coder applies momentary earth to the pulse conductor in order to effect a switching operation at the repeater being used on the call. In the case of routine tests this earth on the pulse conductor operates relay EP, over a circuit from the pulse conductor, bank contact and wiper 105 of the secondary distributor, bank contact and wiper 10a of the primary distributor, conductor 103, working contact of armature 63, conductor 102, working contact of armature 101, conductor 287, winding of relay EP to battery. The operation of relay EP opens the locking circuit of relay Z and, as the initial energizing circuit of relay Z is broken when relay CS operates, relay Z releases. The guarding conductor of the coder is now reguarded through the low resistance winding of relay PS as before. If earth is not received on the pulse lead after the code is sent, relay EP will not operate, consequently relay Z remains locked and as soon as relay TSR operates in the manner previously described, an alarm circuit is closed from earth, working contacts of armatures 288 and 280, lamp 289, low resistance upper Winding of relay FA to battery.

Returning now to consideration of the further progress of a successful test, the number 4244i will be displayed and after a short pause this number will be extinguished and the test switch stepped to its second position in the manner already described. The circuit of relay SDD, Fig. 6, is therefore opened and that of relay DC completed, from earth, wiper of the test switch, second bank contact, normal springs of key 251, conductor 252, winding of relay DC to battery. Moreover, the release of relay CD again completes the circuit for relay SS at the back contact of armature 61 and relay SS upon operating, at armature 130 connects earth to conductor 131, bank contact and wiper 132 of the control switch CS, interrupter sarings and magnet Dhila to battery so that the control switch wipers will be advanced to the ninth set of contacts. The impulse springs 81 are now extended to the two-step relay PA at armature 83, and when relay PS1 has operated in l-inown manner, pulses are transmitted to the sender switch driving magnet D313 and the sending switch wipers will therefore be stepped round the bank. The operation of relays SA, RA and RE new take place as already described and. causes earth impulses to be connected to the pulse conductor to the coder. When four such impulses have been sent, earth is extended over wiper 100 of the control switch, 9th bani-1 contact, conductor 107, resting contact of arn'iature 108, conductor 109, bank contact and wiper 110 of the sending switch and conductor 111 to operate relay rlZ. The sending switch will then be brought to a normal position; the pause timing switch will be operated to ensure the correct pause between digits and the control switch will be advanced one step. The sending switch will then again rotate and earth pulses will be applied to the pulse conductor to the coder. It rill now be noticed that due to the operation of relay DC, eight such pulses will be sent to the coder before relay SZ is operated and the sending switch is brought to its normal position, the circuit to operate relay SZ being new from earth, wiper 106 of the control switch, 10th bank contact, con- L5, working contact of armature 126, ng contact of armature 253, conductor 1 to bank 110 of the sending switch and tl nce to relay SE, and for succeeding operations of the sending switch this circuit is again completed over contacts 11, 12 and 13 of the control switch which are coinmoned together and to contact 10. The digitsimpulsed to the coder for this position of the test switch are therefore 418888, the digit 4c effecting the determination of the junction compensating resistance value and 8888 being equivalent to a subscribers number. The control switch will now be on the 14th set of contacts and relay SC will operate, and as relay SDD is normal relay DL will be operated immediately from earth, wiper 106 and 14th bank contact, conductor 127, resting contactof armature 255, conductor 256, winding of relay DL to battery. As the delayed sending feature has already been tested on the first test, it is eliminated on succeeding tests by operating relay DL as soon as the control switch is stepped after the last digit is sent into the coder. The operation of relay DL disconnects battery and earth through the winding of retard TR, from the line leads from the coder and thereupon the coder trapsmits the number in the form of coded pulses. Due to the operation of relay DC, battery for display lamps 8 is now fed through resistance 20?, working contact of armature .439 and conductor 2 10, while battery for lamps 4 is now through the winding of relay lVN, conductor 238, the working contact of armature 206 and conductor 205, so that if any lamp other than 8 be lit, the wrong alarm circuits it the number is incorrectly or inadequately received, are identical with those already described and W111 be readliy followed from the previous description. In

this case however the digit 8 is being transmitted, the corresponding code being a light positive pulse, a heavy ne ative pulse and another heavy negative pulse. As previously pointed out, heavy negative pulses operate both relays HN and LN, and the relays which are operated in the first storing group to give the digit 8 are MW, MK and MZ, a similar combination bein set up in other storing groups. Relay I Fig. 6, also responds to the heavy pulses, but its operation is ineffective at this stage. At the successful conclusion of the reception and display of the number 8888 the test switch is advanced to the third set of contacts, the third indicating lamp is lit from bank 68, and a circuit is completed for relay NC from earth, wiper 50 and third bank contact of the test switch, normalcontacts of key 257, conductor 258, winding of relay NC to battery.

The function of the coder which it is now desired to check is the correct addition of re sistance to the junction during the pulsing period to compensate for differences in length of the junctions to which the coder may be connected, so that the coded pulses may always be effective over substantially the same junction resistance. As is described in Patent No. 1,716,563, this compensation is effected by sending an additional digit into the coder previous to the subscribers number, this digit being previously determined by the trunking scheme. This digit may conveniently be either 1, 2, 3 or 4, so that if the junction over which the call is to be completed is, for example, in the neighbourhood of maximum resistance, the extra digit 4 is sent and the coder circuit is arranged so that this digit brings no additional resistance into the pulsing circuit. Should the junction be of minimum resistance, the digit 1 will bring sufficient additional resistance into the pulsing circuit so that the junction may be of substantially the same total resistance as before, while digits 2 and 3 serve to effect intermediate adjustments for intermediate junction resistances. The operation of relay NC maintains relay DC at armature 260, and at armatures 164 and 161 connects the upper winding of relay LD across the line leads from the coder in place of the relays LN, LP and EN. The operation of sending a number into the coder now proceeds as before, the first, or compensating digit being 4 as before, while due to the. operation of relays NC and DC the subscribers number is now 7 7777. The circuit to stop the sending after 7 pulses have been sent may be traced from earth, wiper 106 of the control switch, 17th bank contact on which it is now resting, conductor 125, working contacts of armatures 126 and 253' to sending switch bank 110 and thence to relay SZ and as the control switch steps after each digit, this circuit is the same for each sending operation due to the cominoning between contacts 17,18, 19 and 20 on bank 106. The number thus transmitted is 7777 preceded as usual by the compensating digit 4. Relays DL and SC operate as soon as the control switch is stepped to the 21st position and thereupon the coder will transmit the code pulses corresponding to the number of two heavy negative pulses and'therefore eight suchpulses in all should be received.

The first pulse received will operate relays ((17. The code for digit 7 consists 1C and LD and at armature 261 relay LD closes [a locking circuit for itself over conductor262 to earth at working contact of armature 197. Furthermore, at armatures 263 and 264 the codedpulses are transferred to the windings of differential relay CR'F. It will now be seen that, due to the operation of relays NC and LD, the decoding relays LN,

LP and I-IN are replaced by the differential relay CRF; accordingly the numbers received will not be displayed on the lamp panel, it

being intended at this stage merely to check the correct operation of the coder circuit in inserting the appropriate value of junction compensating resistance in response to the initial digit dialled. The circuits over which the coded pulses are now received may be traced from the negative line from the coder, bank contact and wiper 131 of the secondary distributor SD, bank contact and wiper 132 of the primary distributor PD, conductor 133, working contact of armature 64, conductor 134, resting contacts of armatures 135 and 136, conductor 137, working contact of armature 138, conductor 160, winding of relay IC, working contact of armature 161, working contact of armature 264, lower winding of relay CRF to battery and also from the positive line from the coder, bank contact and wiper 144 of the secondary distributor SD, bank contact and wiper 143 of the primary distributor PD, conductor 142, working contact of armature 62, conthere are eight pulses in all, this circuit will be closed eight times and consequently the counting switch will be advanced eight steps so that the wipers are now on the ninth set of contacts. Earth will then be extended from wiper 268,. 9th bank contact, conductor. 269, winding of relay L1 to battery so that relay LI- operates The operation of relay LI. prepares av circuit at armature 271 to permit. the operation of relay EP with the earth. received from. the coder on the pulse conductor. as soon. as the complete code hasbeen sent,.and as soon as relay EP has oper ated. earth is extended from working contact of. armature 290, conductor 291, working contact 035 armature 292,. resting contact of armature 2 17, conductor 21-8, winding of relay CD to battery. The operation. of relay CD energizes the driving magnet of the test switch and. also effects the necessary circuit changes in a. manner already described so that the next test can. proceed. Moreover earth is extended from resting. contact of armature 300,v conductor 301,. bank. contacts and wiper 302 of. the counting'switch CGS and thence to the driving. magnet Dlilfi by way of interrupter springs 305 to cause the wipers ofv the counting switch to be moved tothe home position, thus breaking the circuit of relay LI which releases. The test switch wipers are now on the 4th set of contacts, the appropriate: lamp lit from bank. 68 and earth. is extended from wiper 50. overnor-mal. springs-of the key 294,

conductor 295,.lower winding of relay CR A to'battery. Relay CHI h; operates, thereupon at armature 296 maintaining relay NC ener.-- gizedg. at armature 135 removing the short circuit fromiresistance 297-, and at armature 108 extending. earth from the control switch wiper 106, conductor. 107 ,working contact of armature 108, resting contact of armature 298,.conductor 299 to the third lead from.

the sender switch bank-1110. The operations ofsending a number into-the coder will now proceed exactly as before described with the exception that due to the operation of relay GRA the initial digit sent to the coder to determine the compensating resistance value. is3 the remainder of the number is as before 777 1. The com ensatin di it 3' serves P D b to bring; into the coder iinpulse'sending circuit a certain value of resistancc' in order to make thecoded pulses effective over substantially a-stand'ard junction value while it will be noticed that the operation of relay CEA has introduced the resistance 297 into the circuit of the differential relay CRF. This resistance is so chosen that it balances the resistance that the coder should includein the impulsing circuit in response to digit 3, consequently when the coder sends out theeight heavy negative pulsescorresponding to 7777, differential relay CRF, this rel'ay again does not operate. The pulses received from the coder cause relay 10 to operate 8 times and consequently the counting switch GGS advances- 8 steps as before, and relay LI thereupon operates and prepares the circuit of relay E? which operates immediately on the conclusion oft-he sending operation. Thereuponrelay GD operatesand the succeeding operations take placein a manner which will be readily followed from the description aleady given.

The test switch is now advanced to the fifth of contacts in readiness for the next test and-in this-position relay CRA is released and relay CRB operated from wiper 50 over normal springs of; key 304 and conductor 305. The operation of relay CRB- introduces resistance 306 into circuit at armature 136; at armature 307 maintains relay- NC operated and at armature 308 extends earth fromwi aer 1'06 of the control switch, conductor 107, working contact of armature 308, resting contact of armature 309, conductor 310 to the secondl'ead to the sender switch bank.

the compensating digit, will therefore be 2 usual. The resistance 306 brought into circuit by operation of relay (IR-B is chosen tobalance that which is brought into the impulse circuit of the coder by the digit 2' and consequently on the coder sending the coded pulses the differential relay CRF does not operate.

On the next test which is carried out in the 6th. position of the test switch, both relays CRA; and ORB are operated, thereby introducing both resistances 80.6 and 297 into circuit, while at the working contacts of armaturcs 108 and 298 earth is extended from the control switch wiper 106 to the first lead from the sender switch bank, so that the'compensating digit is in this case 1, followed thereafter by 7777. As in the previous tests, the resistances 306 and 297 are of a value to balance that included in the coder pulsing circuit bythe initial digit 1, and on the consequent sending of the coded pulses the differential relay CRF still does not operate. It follows therefore that during any of the precedingtests, if'the relays in the coder cirand the circuit is switched to the- The first digit impulsed into the coder, that is 

